With the rapid spread of a vehicle, an increase speed of the number of vehicles is significantly larger than an extension speed of a road network according to statistics.
Accordingly, as a V2V collision risk on a road increases day by day, consumer's desires for a more stable and intelligent vehicle have merged with a development progress of vehicle related industries, and as a result, various intelligent safety systems have been developed and applied.
In particular, a lot of researches have been conducted into a collision warning and avoidance between an own vehicle and a preceding vehicle and the resulting V2V distance control system can secure a more safe and fresh driving environment under a complicated road situation.
However, since there are no definite solutions for a time and a method of the collision warning and avoidance, tasks that a lot of researches and tests should be performed now and forever have been scattered.
The V2V distance control system sets a speed at which a driver intends to drive the vehicle and a control means controls a throttle actuator and a brake actuator by analyzing various load conditions which influence the vehicle and a vehicle speed to maintain driving according to the set speed.
A time gap is set, which can maintain a safe driving distance.
As described above, while the vehicle is driven at a constant speed, the control means senses a distance from the preceding vehicle by a distance sensing means installed at a predetermined front location of the vehicle to extract a relative distance and a relative speed between the own vehicle and the preceding vehicle.
When the extracted relative distance and relative speed are states of a relative distance and a relative speed having a collision risk, the set time gap is applied to perform a distance control.
The safe driving distance is calculated under a condition of (time gap×own vehicle speed).
In this case, when a threshold braking distance between the own vehicle and the preceding vehicle is arithmetically calculated and the calculated threshold braking distance is within the safe driving distance, the safe driving distance should be secured by a braking control by controlling the brake actuator or an engine torque reduction control by controlling the throttle actuator.
As described above, the speed of the own vehicle is decreased by a control for maintaining the safe driving distance, and as a result, when the relative distance between the own vehicle and the preceding vehicle increases, engine torque is restored by controlling the throttle actuator, and as a result, the speed of the own vehicle is restored to the set constant driving speed.
The V2V distance control system mounted on the vehicle in the related art cannot be controlled by the driver because the time gap for maintaining the safe driving distance is set to a predetermined value.
The driver is adapted to set the time gap in three steps (Far/Med/Close) depending on the system, but difficulty and inconvenience in the operation are accompanied in setting the time gap while driving, and as a result, safe driving is hindered.
For example, if the set time gap is 2 seconds/1.5 seconds/1 second, when the own vehicle is driven at 100 km/h, the own vehicle is driven with an interval from the preceding vehicle by 55 m/42 m/28 m.
Accordingly, when the condition is considered, a minimum stop distance of the vehicle that is driven at, for example, 100 km/h is 38 m and the distance has a higher priority than a distance (55/42/28 m) set by the driver for safety of the driver.
However, it needs to be considered that a friction coefficient between a tire and a ground surface is not continuously 1.0.
The friction coefficient between the tire and the ground surface has a feature which varies according to a state of the road surface.
The friction coefficient is large in variation even depending on a type (asphalt, concrete, an unpaved road, and the like) of road surface, a type (carcass/radial) of tire, and a tire thread shape and an aging degree.
That is, a difference in friction coefficient between the case where the vehicle is driven on the concrete with new tires on a fine day and the case where the vehicle is driven on the asphalt with old tires on a rainy day is approximately twice as much, and as a result, a difference in maximum deceleration is also twice as much.
The V2V distance control system applied to the vehicle in the related art fixes the maximum deceleration to 9.8 m/s2 under a condition in which the friction coefficient between the condition of the tire and the road surface is not sufficiently reflected at the time of calculating the minimum safety distance of the driver by considering the maximum deceleration while driving not to secure an optimal safety distance.
Accordingly, the V2V distance control system has a disadvantage that the collision between the preceding vehicle and the own vehicle cannot be avoided under an emergency situation.